Various products and formulations have been used throughout the years for the treatment of or use on human skin in the attempt to keep the skin in a smooth supple condition or to prevent some condition or unpleasant characteristic. Many of the formulations used to make personal care products are in the form of emulsions. The preparation of aesthetically acceptable emulsion products involves attention to properties such as tackiness, greasiness, lubricity, feel, and safety. Silicones are most desirable as components of water/oil emulsions used to make personal care products because they impart a velvety smooth quality, adhere well to the skin, spread easily, and dry quickly without a heavy or greasy feel. However, until just recently it has been very difficult to use silicone in appreciable amounts in water in oil emulsions since the resulting emulsions are unstable and usually break within hours or days. This problem was partially solved with the discovery of a group of polyoxyalkylene-polysiloxane copolymers which are described in U.S. Pat. No. 4,698,178. These compounds, sold by Goldschmidt Corporation under the trade name ABIL B 9806, ABIL WE-09, ABIL B 9808, or ABIL WS-08, function as emulsifiers in silicone containing water in oil emulsions. The use of these compounds results in emulsions which have increased stability and do not readily disintegrate into separate water and oil phases. The level of emulsifier is directly proportional to the dispersion of the water phase in the oil phase i.e. the greater the level of emulsifier the greater the number of water droplets dispersed in the oil phase. A water in oil microemulsion results when the water is dispersed throughout the oil phase in the form of "micro" droplets so that the droplet size is smaller than the wavelength of light. Microemulsions are very desirable in personal care products because they are excellent vehicles for enabling penetration into the skin of active ingredients which would not normally penetrate the stratum corneum. Moreover, clear microemulsions are desired since an opaque, pearlescent, or cloudy appearance is not always pleasing particularly if the product is used as a base for personal care items where a very fresh, clean and clear look is desired, such as sunscreen products, skin hydrating moisturizers or antiperspirants. As a rule, to achieve a clear water in oil microemulsion containing silicones the addition of very high levels of emulsifiers is required, in the order of 20% or more. This is not desirable since organo silicone emulsifiers are very expensive. At the high levels required to achieve a microemulsion these emulsifiers may cause irritation to the skin as well as resulting in a composition which is very tacky when applied to the skin even though organo functional polysiloxane type emulsifiers exhibit less tackiness than the conventional water in oil emulsifiers. However, if the level of emulsifier is decreased to too low a level to minimize expense, a loss of stability and aesthetic appearance results, the composition becomes cloudy and opaque, and the viscosity of the composition in turn decreases resulting in an emulsion with less than desirable consistency.
Microemulsions of a high consistency are difficult to formulate. The thickening agents which are used to control the rheological properties of conventional emulsions will more than likely prevent the formation of microemulsions. It is known that the addition of salt to water in oil emulsions based upon organo functional silicone emulsifiers increases their stability but the amounts recommended by the prior art are quite small, generally 1 to 2 percent. However, these small levels are sufficient only to enhance the viscosity and stability of microemulsions of low consistency. Thus, to date most microemulsions exist in the form of lotions since cream type microemulsions do not have the luxuriant "feel" and safety required for marketable cosmetic preparations.
There is therefore a need for silicone containing water in oil microemulsions which are not opaque or cloudy, have a pleasing appearance and firm consistency, and are not tacky, irritating to the skin or expensive.